Method and apparatus for coating particles



Nov. 26, 1963 A. L. HElSER/JR, ETAL METHOD AND APPARATUS FOR COATING PARTICLES Filed Feb. 26, 1960 2 Sheets-Sheet 1 Inventors Albert L. Heiser, Jr.

Werner Lowenthal Robert E Singiser Nov. 26, 1963 A. HEISER, JR., ETAL 3,112,220

METHOD AND APPARATUS FOR comma PARTICLES Filed Feb. 26, 1960 2 Sheets-Sheet 2 Inventons Albert L.Jleiser,Jn Werner Low'enfl'zcll Robert E.Singi$er United States Patent Illinois Filed Feb. 26, 1960, Ser. N 11,364 2 Claims. (Cl. 1171G(P) This invention relates to a method of coating discrete particles with a liquid and more particularly to a method of coating tablets with a liquid coating suspension or solution.

Many attempts have been made in the pharmaceutical field to coat tablets without the use of the familiar pan coating procedure and the consequent requirement of oven drying. One of such methods is the so-called airsuspension method whereby air is forced up through a bed of tablets which are enclosed in a chamber so as to suspend them and while so suspended to coat them with a coating fluid by introducing the coating in the form of a spray. This method has had many disadvantages as the tablets to be coated are placed in a turbulent air stream and thereby collide with the side of the chamber and with each other causing breaking and chipping of the tablets. In some instances when applying the coating fluids the tablets stick together and an elegantly coated tablet is not obtained. In accordance with the present invention, these problems are overcome by presenting a novel air-coating method which provides a smooth and uniform pattern for the tablets as they are being coated.

The method of the present invention comprises forming a columnar bed of tablets or other particles to be coated. Preferably the bed is substantially greater in height than it is in the horizontal cross-sectional dimensions. An air stream is directed upwardly through a portion of this bed with suflicient force that the tablets in that portion move upwardly forming, in effect, a fluidized spout of tablets up through said portion. The spout extends above the top of the bed with the tablets falling therefrom back onto the top of the bed. In the parts of the bed adjacent the spout the tablets move downwardly.

The coating liquid is atomized and introduced into the upwardly moving stream of air. The term coating liquid is used herein to refer to liquids, liquid solutions, liquid suspensions and the like. 'Iihe atomized liquid is deposited on the tables in the upwardly moving spout with the deposited liquid being dried by the air. To some extent the air will diffuse through other parts of the bed to further the drying of the coated particles in those other parts.

The present method also provides the previously described advantages when it is desirable to coat particles other than tablets such as the coating of granulations, seeds, candies or the like.

One of the objects of the present invention is to provide an improved method and apparatus for coating tablets with a coating fluid without the need of pans or the like or the drying of the coated tablets in an oven.

Another object is to provide an air system method and apparatus for coating tablets whereby a uniform and smooth pattern is established for the coating and drying of the tablets and thereby reducing chipping and breaking of the tablets and providing a uniform coating on all of the tablets.

A further object of the present invention is to provide an improved method and apparatus for applying a plastic coating to discrete particles utilizing a liquid plastic whereby sticking of the tablets during the coating process is eliminated.

Still another object is to provide a method and apparatus which will coat particles fast and eificiently.

A still further object is to provide a method and apparatus for uniformly applying a coating fluid on solid particles in a fast and eflicient manner.

The method of achieving the foregoing objects of the invention will be readily appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings showing the embodiments of the invention wherein:

FIGURE 1 is a side elevational view of an apparatus for carrying out one embodiment of this invention with some portions broken away and other portions in vertical section to illustrate the pattern of the particles in the chamber.

FIGURE 2 is a side elevational view of a modified embodiment of a coating chamber to be used in conjunction with the apparatus in FIGURE 1.

FIGURES 1 and 2 describe alternative apparatus for carrying out the heretofore method that we have invented.

In one embodiment of the invention illustrated in FIG- URE 1, the apparatus is composed of a cylindrical colum nar chamber 1t} having an upper end open to receive an adaptable exhaust duct 11 with a thermometer 12 disposed therein. Chamber 10 has a conical section 13 at its lower end with a door 14 provided therein for discharging particles 15 from chamber 10. A sleeve-like joint 16 is placed around the lower end of chamber 10 for connecting chamber 10 with conical section 13.

Conical section 13 rests at its lower end on support block 17 which has a circular passageway 18 in axial alignment with chamber 10. The diameter of conical section 13 at the point where it contacts chamber 10 as well as the diameter of the chamber itself is 6 inches. At the point where conical section 13 rests on support block 17, conical section 13 has a diameter of 1% inches. This means that chamber 10 has a cross-sectional area approximately ten times that of conical section 13 at its narrowest dimension.

A screen 19 is disposed in passageway 18 for preventing particles 15 from falling out of chamber 10 when the apparatus is not in operation. Support block 17 at its lower surface is in engagement with air duct 20 having an enlarged elbow portion 21 immediately below block 17 and a constricted portion '22. Connected to constricted portion 22 is a heat exchanger 24 wherein the heating coils are connected to a steam line 25 [having a pneumatic control valve 26. A condensate line 27 also is connected to exchanger 24. A blower 23 is connected to heat exchanger 24 by a pipe 75.

A temperature sensing element 2.9 is located in elbow portion 21 and is connected to pneumatic indicating controller 30. Temperature control is effected via controller 30 and valve operator 28 which actuates valve 26 in steam line 25. A Pitot tube 31 is disposed in constricting portion 22 for measuring air velocity in duct 22. Pitot tube 31 is connected by tubes 32 and 33 to manometer 34 to register the velocity thereon. Disposed in pipe is a damper 35 for controlling the amount of air from blower 23 through air duct 20.

Positioned below chamber 10 in the enlarged elbow portion 21 of air duct 20 is pneumatic atomizing spray nozzle 36 having a l i inch diameter to which is connected air line 37 attached to a source of compressed air, and a fluid supply line 38. A fluid supply chamber 39 containing coating fluid 44) is connected to supply line 38. A strainer 41, a needle valve 42 and a thermometer 43 are provided in fluid supply line 38. Disposed in the lower portion of supply chamber 39 is a heating coil 44 having a steam line 45 with valve 46 and a condensate line 47 attached thereto. Supply chamber 39 is sustained by supporting block 48 accommodating supply 3 line 38, steam line 45 and condensate line 47 therethrough. An inlet pipe 49 with valve 50 and funnel 51 is disposed in communication with the upper portion of supply chamber 39 and is secured in cover member 52. A nitrogen supply line 53 with valve 54 is disposed in the same manner as inlet pipe 49.

The modified device of FIGURE 2 is composed of a cylindrical chamber 55 and like chamber 10 of FIGURE 1 has its upper end open to receive an adaptable exhaust duct 56 having a thermometer 57 disposed therein. Chamber 55 has at its lower end an oblique conical section 58 with one side perpendicular to the base of the cone. A door 59 is provided in conical section 58 for discharging particles 60 from chamber 55. A sleeve-type joint 61 is placed around lower end of chamber 55 for connecting chamber 55 with conical section 58. Oblique conical section 58 rests at its lower end on support block 62 which has a circular passageway 63 in vertical alignment with chamber 55. A screen 64 is provided in pas sageway 63 for preventing particles 60 from falling out of chamber 55 when the apparatus is not in operation. Support block 62 at its lower surface is in engagement with air duct 65 which is similar to air duct 20 in the apparatus of FIGURE 1. Air duct 65 serves as a housing for spray nozzle 66 to which is connected fluid supply line 67 and an air line 68 for compressed air. The dimensions of the modified device are the same as those given for the preferred apparatus.

EXAMPLE I On method of coating particles in the apparatus in FIGURE 1 is carried out by closing all the valves in the apparatus with the exception of valve 50 and introducing a diluted coating suspension through funnel 51 and inlet pipe 49 into fiuid supply chamber 39. The coating suspension employed herein is of a yellow color and has the following formula:

Gm. Cellulose acetate phthalate 60.00 Propylene glycol 18.68 Sorbitan monooleate 6.00 Alcohol SD, 3A, 200 proof 231.30 Dye, Yellow D & C, Lake 30.00 Titanium dioxide 20.00 Saccharin sodiurm 1.00 Ethyl vanillin 4.00 Polyethylene glycol 6000 140.00

Acetone q.s. 1000.00 ml.

The cellulose acetate phthalate is dissolved in 200 ml. of acetone and to this mixture is added the propylene glycol and the sorbitan monooleate. The yellow dye, titanium dioxide, saccharin and ethyl vanillin are added to a ball mill and sufiicient acetone is added to cover balls. After milling for 24 hours, the milled ingredients are added to the previously described mixture. The polyethylene glycol is melted in a portion of the alcohol and is also added to the previously composed mixture together with the remainder of the alcohol. Acetone is subsequently added to bring the suspension to a total volume of 1000 ml.

Prior to the introduction of the coating suspension into chamber 39', it is diluted with two liters of acetone to give a total volume of 3 liters and the diluted suspension pro-warmed to a temperature range of 4045 C.

After the diluted solution is placed in supply chamber 39, valve 50 is closed to make a closed unit and steam is supplied through steam line 45 sufficient to bring the coating fluid 40 to a slow rolling boil which is a temperature of about 55 C. With coating fluid 40 being maintained at a rolling boil, valve 54 is opened and nitrogen under a pressure of 5-7 p.s.i. is introduced through line 53 into supply chamber 39. A source of compressed air is attached to air line 37 at a pressure of approximately 25 p.s.i. Exhaust duct 11 is removed from the top of chamber and 4 kg. of tablets are placed in the chamber. The tablets employed in. this particular instance are ovaloid in shape having a width of approximately .205 inch, a length of about .388 inch and compressed so that 10 tablets equal 1.56 g. Exhaust duct 11 is subsequently replaced. Pneumatic indicating temperature controller 30 is set at a control point of 140145 F. and it automatically adjusts pneumatic control valve 26 to provide the desired temperature range in air duct 20. The temperature is shown on indicating controller 30.

Blower 23 is then turned on and damper 35 is adjusted to a position that tablets 15 in chamber 10 assume a uniform pattern as indicated by the arrows and which will be explained more fully later. With tablets 1S assuming the designated pattern, needle valve 42 is opened and with compressed air as previously described flowing through air line 37, coating suspension 40 is sprayed by means of nozzle 36 into conical section 13 and chamber 10. Coating suspension 40 is applied at such a rate that the temperature of the air leaving chamber 10 by way of exhaust duct 11 and as indicated by thermometer 12 does not fall below F. The rate should also be suflicient that the coating suspension 40 is applied in approximately a 15-minute period. In this particular operation screen 19 is of 8 mesh size so as to allow the maximum amount of air to enter chamber 10 and yet prevent tablets 15 from falling into air duct 20.

It will be noted by means of the arrows in chamber 10 that tablets 15 during the previously described process assume a spouting effect. Specifically, tablets 15 are carried by means of the air pressure from duct 20 and also from nozzle 36 substantially vertically upward through the tablet bed at a relatively high velocity through a minor portion of the bed and to form a spout therein. The upwardly carried tablets 15 rise to a height of about 5-6 inches above the major more dense portion of the bed to form a fountain-like effect and then fall outwardly and downwardly to form the major portion. As the tablets 15 form the major portion of the bed they move at a relatively low velocity downwardly and toward the minor spout portion at all levels along the spout and the cycle is repeated.

While tablets 15 are assuming the previously described pattern, the tablets in the spout area near the lower portion of the bed are partially sprayed with coating suspension 40. The partially coated tablets then rise through the bed and by doing so are dried by means of the air in the spout area and also by the air being forced up through the major portion of the bed. It should be noted that because of the geometric structure of chamber 10, the air disperses in a horizontal manner towards the sides of the chamber at a rate which is proportionate to the height of the bed. This elfect takes place even though passageway 18 and nozzle 36 tend to direct the air in a substantially vertical manner through the tablet bed. That is to say, that near the upper regions of the tablet bed a high degree of aeration is taking place in the major portion of the bed and thereby drying of the coated tablets is facilitated. This aeration aspect as well as the air in the spout area and the tablet movement therein prevents the coated tablets from sticking to each other. It should also be observed that by employing this uniform pattern for coating tablets the tablets are treated gently at all times during the operating and chipping and breaking is kept at a minimum. Also, because of the uniform pattern, the tablets receive a very uniform coating.

When the coating operation is completed, valve 42 is closed, the steam is turned 011 in steam line 45 of coating chamber 39. The tablets 15 are continued in the patterned motion for purposes of drying until the temperature indicated by thermometer 12 reaches about F. The steam in steam line 25 for heating the air in air duct 20 is turned off and the tablets are continued in the patterned motion for about 5-10 minutes more to elfect suflicient drying. During this 5-l 0-minute interval an increase in temperature will be noted after all of the acetone has evaporated. An increase in temperature can cause sticking and in order to prevent such, it is desirable to stop the drying operation or to introduce cold water into heat exchanger 34 and thereby provide a source of cool air in air duct 20. After the tablets are dried, they are removed from the chamber 10 by means of discharge door 14. The

ment sends the tablets 60 up along the side of chamber 55. In all other respects, the movement of the tablets 60 assume the same pattern as that described for the method in FIGURE 1.

fluid supply chamber 39, fluid supply line 38 and nozzle 5 EXAMPLE H 36 can be cleaned with a solvent such as acetone.

The apparatus of FIGURE 2, for carrying out a modified This example illustrates 24 representative runs employembodiment of the present invention is operated substang a us plas c Coa ing S HtiOIIS, and employing partially the same as that described in the procedure in opi l f various sizes, amounts and im Th erating the apparatus of FIGURE 1. The m in differen 10 components of the various formulae employed are given in between the two methods is that a modified pattern is em- Table I and th ata f r the ru s iS giv n in Ta le II. In ployed while coating and drying tablets 60. The pattern runs 1-22 the center-spout pattern described in Example employed as shown by the arrows is in eifect a side-spou I and shown in FIGURE 1 of the drawings is employed. rather than the center-spout previously employed in In the case of run 1 a 10-inch diameter column is used in FIGURE 1. The side-spout efiect is accomplished by 15 place of the 6-inch diameter and in runs 3 and 4 a 15-inch utilizing an oblique conical section 58 at the bottom of diameter column is utilized. Runs 23 and 24 employ the chamber 55 and vertically aligning nozzle 66 near the side-spout pattern previously described and shown in perpendicular side of conical section 58. This arrange- FIGUREZ of the drawing.

Table I Formula 1 2 3 4 5 6 7 s 9 10 11 12 13 14 15 16 17 1s 19 Cellulose Acetate Phthalate (gm) 60.0 100.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 60.0 15.0 15.0 15.0 10.0 30.0 62.6 15.0 Cellul se Acetate (gm). 30.0 15.0 Ethylene-maleic anhydride copolymer m. Ethylene-maleie anhydride copolymer (MW 25,00030,000) (gm. Propylene glycol (gm)- lyceryl monooleate (gm) Propylene glycol monolaurate (gm) Polyvinylpyrrolidone m. Sorbitan Monooleate (gm) Alcohol, ethyl, 200

Dye, Yellow D & 0,

Lake #5 (gm) Dye, Blue FD dz 0 #2 (gm) Dye, Blue D dz 0 #9 (gm) Dye, Blue FD dz C #1 m. Dye, Yellow D & C

#11 (gm) Dye, Yellow FD & C

#5 m. Titanium Dioxide m. Saccha)ri n Sodium 1n. Ethyl Vanillin (gun)... Polyethylene Glycol Oornarin (gin) 'lannic Acid (gm.).. Charcoal Willow Powder gm.) Glyceryl onostearate m. Iron Oxide Venetian Red (gm.) Dye, Red D dz 0 #36 1 gm.) Liquid Petrolatum (gm) Acetone q.s. ad. (ml.)" Additional Acetone q.s. ad. (ml.) Alcohol Ethyl 200 Proof (ml.)

7 EXAMPLE III This example represents the coating of tablets with a coating solution having sugar particles suspended in the coating solution. The procedure is basically the same as that described in Example 1. Three kilograms of ovaloid- 8 In a like manner, the plastic resins and formulations described in US. pending patent application 765,338, now Patent No. 2,954,323, of which one of the applicants is a co-inventor can be utilized and still fall within the scope 5 of the present invention.

Table II Total Pres- Total Weight Total Foun- Volume sure on Nozzle Time Type of of 10 Weight tain Inlet Outlet Coating of For- Temp. oi Coating Preswith Run Particles Parti- Shape Dimensions of Par- Height Temp. 'lemp. Formula Coating Formsure Drying cles ticles (lnch- (F.) (*F.) mula Em- Formula ula (p.s.i.) (Min- (gm.) (kg) es) ployed (p.s.i.) utes) (Liters) 1.44 Convex-.. 962 punch size-.- 20.0 8 135 78 1 11.0 55C.--. 5 25 50 1. 44 -do 95 2" punch size--- 4. -0 129-30 80 1 2. 2 50C- 7 30 25% 5.05 %2 punch Size 40.0 12 145 80 2 40.0 warm... 7-10 32 58 5. 05 %2 punch size-- 30. 0 16 140-45 86 2 30.0 do 20 32 53 7. 74 d0 32" punch Size 4. 0 149-45 90 3 2. 3 boiling. 6 35 16% Ilength: .4022 1 2. 19 Ovalotd-.. Width, 2260 4. 13.. 38 96-100 4 1. 2 do- 4 30 1714 2.10 -.do 55,1-: 4. 0 140-411 82-88 5 .0 .-.do-..-. 5 25 w 2. 27 Convex- 552" punch s ize- 4. 0 132-38 96-100 9 1. 4 (lo- 4 30 17% 19 ovaloidun {lvsalgttllilzi 0 5-0 116-22 92 l 2.0 ...do 3 22 29 1. 78 Convex. ,46 punch s i ze- 4. 0 5 120 92-98 8 1. 5 62C. 6 25 27 2.19 Ovaloid--- {395 5 4. 0 545 12540 94-98 9 2. 1 boi1lng. 5 25 22 ,2 2.19 do {12 5,55 5 4. 0 130 90 10 2.1 do 4 25 24 1.78 Convex. 4. 0 5-6 85 11 2. 0 do..-.- 4 35 21 H 1.99 Ovalold--- 3.0 4% 146 119 12 2. 0 60C. 3 22 25 1. 99 do- 3.0 6 142 122 13 2. 0 52C. 3 22 33 10--. --do---.- 1. 99 do- 3.0 4% 146 110 14 2. 0 56C..-- 3 22 20 17--- .-.-d0 2.19 do 3. 0 5-6 182 149 2. 0 boiling-- 3 22 32 18--- --do 2. 47 do 3.0 5-6 145 104 10 2. 0 -do 3 25 20 1. 78 Convex. 4. 0 5-6 135-45 82 17 2. 0 ---do 5 30 20% 1.78 do 540" punch size.-- 4.0 5-6 120-30 93 18 2.0 4 2.02 R0und--- 934-942 4. 0 140-45 70 2 4. 0 46C- 6 30 23% iameter.

ea 22--- Ngn-rareil 1 16 do 12-20 mesh 3.3 26 142 70-80 3 1 2 43C..-- 3 22 31 cc s 23--- Tablets. 1. 79 Convex--- 54a" punch size--- 3. 0 8-10 150 126 19 2. O 54C..-- 3 22 30A do-.-.-. 4.00 .do %2" punch size 3.0 8-12 125-30 80 4 3.0 60C..-. 0 25 my.

1 Not taken. I Mg. 3 Only 1000 ml. acetone was used for diluting.

shaped tablets having a length of .4022 inch, a width of .2260 inch and ten of which weigh 2.19 g. are coated with a bright lemon yellow solution as represented by coating Formula Number 1 of Table I modified in that 750 ml. acetone is used in diluting 1250 ml. of the concentrated coating solution. Two liters of this formulation are employed into which is placed 200 g. of powdered sugar, 200 mesh. The coating solution with the sugar suspended therein is applied over a period of 19 minutes with a drying time of 4 minutes. The temperature of the solution is 64 C. while the air inlet temperature is 137 F. and the air outlet temperature is 110 F. Pressure on the solution is 8 p.s.i. and 22 psi. through the nozzle. This procedure provides a method for building up a tablet and also smoothing over rough edges and corners to give an elegantly appearing product.

Other formulations containing cellulose acetate phthalate such as those described in US. 2,881,085 can be employed in this invention by diluting the formulations given therein in the range of one part coating solution to /2-2 parts acetone. For example: in Example I, of the previously mentioned patent, instead of diluting with acetone to 500 m1., dilute with acetone to 1000 ml. Also, in place of acetone, other solvents such as alcohol, isopropanol, methylethylketone and mixtures thereof can be employed.

Further, in place of the cellulose acetate phthalate resin formulations described and employed herein, other cellulose esters of lower aliphatic monocarboxylic acids can be substituted as well as lower alkylmethacrylates, copolymers of lower alkylacylates with lower alkylmethacrylates and copolymers of lower alkylmethacrylates with methylacrylic acid, and also a polyvinylpyrrolidone-vinyl acetate copolvmer.

The conventional aqueous sugar-coating solutions containing cane sugar as represented by a 25-50% concentration and commonly known as simple syrup can be applied in the manner previously described in applying the plastic resin coating fluid.

It should be understood that many modifications can be made in operating the apparatus described in FIGURES 1 and 2 depending upon the size, the weight, and the number of particles to be coated. For example, when employing the apparatus in the specific examples previously described, the pressure range on fluid in fluid supply chamber 39 can vary from about 0-25 p.s.i.; the air pressure on spray nozzles 36 and 66 can vary from about 20 to 70 p.s.i. The heating coil 44 for heating fluid 40 need not be utilized. Also, the heating coils in heat exchanger 34 need not be employed or can be regulated so that a temperature as high as 200 F. can be attained in coating chambers 10 and 55, depending upon the coating material used, application rate, air velocity, etc. The application rate can also vary depending on the previously mentioned factors from a fraction of an hour to an hour or more.

In some instances to insure a more elegant-appearing tablet, the tablets may be pre-warmed before placement in the coating chamber or they can be pre-warmed therein by allowing warmed air at the desired temperature to flow through the chamber without the previously described pattern being formed.

The foregoing examples describe the application of one coating fluid to particles. Through the novel method of this invention two or more different coating fluids can be applied to the same particles in sequence with a minimum delay in time.

In FIGURE 1 a Pitot tube 31, connecting tubings 32 and 33 and a manometer 34 are described. This apparatus is not essential in operating the coating apparatus of the present invention and is employed to measure air velocity where the pattern or tablets in the bed cannot be easily visualized. By knowing the velocity of the air, the weight, shape, and size of the particles and the dimensions of the coating chamber, the speed of the blower can be regulated to give the desired spouting effect.

It should be pointed out that the distance the particles rise above the tablet bed in forming the fountain-like eifect will vary according to whether the tablets are dry or wet (all other factors being the same). When wet, the particles rise higher and when dry, lower. This is probably due to the fact that friction is reduced when the surfaces of the tablets are Wet.

Others may readily adapt this invention for use under various conditions of service by employing one or more of the novel features disclosed or equivalents thereof. As at present advised with respect to the apparent scope of our invention, we desire to claim the following subject matter.

We claim:

1. A method or" coating particles of a columnar bed of particles, comprising the steps of: providing a columnar bed of particles, said columnar bed of particles consisting of a vertically extending major portion and a vertically extending minor portion, said minor portion being substantially smaller than said major portion, directing a stream of gas upwardly through said columnar bed of particles to form an upwardly moving spout of particles so that said minor portion of said columnar bed of particles spouts upwardly, only said minor portion being supported by said stream of gas, the uppermost particles of said upwardly spouting minor portion being carried upwardly beyond the columnar bed and outwardly of said minor portion of said columnar bed and then falling downwardly onto the major portion of said columnar bed, said major portion of said columnar bed moving downwardly as particles of said major portion enter said minor portion and are spouted upwardly by said stream of gas, and introducing an atomized coating liquid along with said stream of gas into said minor portion of said columnar bed, whereby said particles of said minor portion are coated and the stream of gas serves additionally to dry the coating liquid on the particles in the minor portion as the particles in said minor portion spout upwardly.

2. In a coating apparatus: a columnar coating chamber of a height sufiicient to hold a columnar bed of particles, the bed of particles consisting of a vertically extending major portion and a vertically extending minor portion, said columnar coating chamber having a lower downwardly tapering portion terminating at a relatively small opening, said lower downwardly tapering portion helping to support said major portion of said bed, means connected to said chamber and communicating with said opening for blowing a continuous blast of gas upwardly through said opening with sufiicient force to produce a spout of particles upwardly through the bed of particles, means for preventing said particles from passing downwardly through said opening, said opening being substantially smaller in cross-sectional area than the cross-sectional area of said columnar coating chamber, said opening being sufliciently small to confine said blast of gas generally vertically to form the vertically upwardly extending minor portion which is substantially less in cross-sectional area than the cross-sectional area of said major portion, an atomizing nozzle disposed along the path of said blast of gas, and means for supplying a liquid coating medium to said atomizin g nozzle.

References Cited in the file or" this patent UNITED STATES PATENTS 2,561,392 Marshall July 24, 1951 2,586,818 Harms Feb. 26, 1952 2,648,609 Wurster Aug. 11, 1953 2,708,622 Stone May 17, 1955 2,768,095 Tadema et a1. Oct. 23, 1956 2,865,868 McKinley et al Dec. 23, 1958 2,986,475 Mesnard et a1 May 30, 1961 

1. A METHOD OF COATING PARTICLES OF A COLUMNAR BED OF PARTICLES, COMPRISING THE STEPS OF: PROVIDING A COLUMNAR BED OF PARTICLES, SAID COLUMNAR BED OF PARTICLES CONSISTING OF A VERTICALLY EXTENDING MAJOR PORTION AND A VERTICALLY EXTENDING MINOR PORTION, SAID MINOR PORTION BEING SUBSTANTIALLY SMALLER THAN SAID MAJOR PORTION, DIRECTING A STREAM OF GAS UPWARDLY THROUGH SAID COLUMNAR BED OF PARTICLES TO FORM AN UPWARDLY MOVING SPOUT OF PARTICLES SO THAT SAID MINOR PORTION OF SAID COLUMNAR BED OF PARTICLES SPOUTS UPWARDLY, ONLY SAID MINOR PORTION BEING SUPPORTED BY SAID STREAM OF GAS, THE UPPERMOST PARTICLES OF SAID UPWARDLY SPOUTING MINOR PORTION BEING CARRIED UPWARDLY BEYOND THE COLUMNAR BED AND OUTWARDLY OF SAID MINOR PORTION OF SAID COLUMNAR BED AND THEN FALLING DOWNWARDLY ONTO THE MAJOR PORTION OF SAID COLUMNAR BED, SAID MAJOR PORTION OF SAID COLUMNAR BED MOVING DOWNWARDLY AS PARTICLES OF SAID MAJOR PORTION ENTER SAID MINOR PORTION 